Polyesters, especially polyalkylene terephthalates, have excellent physical and chemical properties and have been widely used for resins, films and fibers. In particular, polyester fibers have a high melting point, and can attain high orientation and crystallinity. Accordingly, polyesters have excellent fiber properties such as chemical, heat and light stability, and high strength. However, polyesters, especially polyester fibers and fabrics, are difficult to dye. The molecular structure and the high levels of orientation and crystallinity that impart the desirable properties to the polyester also contribute to a resistance to coloration by dye compounds. Also contributing to the difficulty in dyeing polyester compositions is the characteristic that polyesters do not have dye sites within the polymer chain that are reactive to basic or acid dye compounds.
Blending of nylon 6 or nylon 6,6 with polyester has been proposed to obtain the benefits of the polyamide acid dye sites in the resulting composition. The high concentrations of polyamide that may be required to impart dyeability in the resulting polyester/polyamide copolymer composition result in decreased physical properties in the polyester/polyamide copolymer and difficulties in processing. For example, Canadian Patent No. 974340 discloses an acid-dyeable polyester composition using polyamides having cyclic, tertiary nitrogen-groups incorporated into polyalkylene terephthalates by blending and extruding the two polymers, and reports that polyamide microfibrils form within the polyester matrix during filament extrusion operations when high polyamide concentrations are used.
Commonly assigned U.S. Pat. Nos. 3,901,853, 4,001,189 and 4,001,190 disclose that many methods have been proposed for improving the acid-dyeability of polyester fibers and filaments by co-polymerization of nitrogen containing modifiers into the chains of polyester molecules, but that they have been inadequate for various reasons. U.S. Pat. Nos. 3,901,853, 4,001,189 and 4,001,190 further disclose that in order to provide good acid-dyeability, the modifier should contain a highly basic nitrogen atom that functions as a dye site but does not adversely affect molecular weight or cause discoloration. Thermal stability, effectiveness at low concentrations and low volatility are important properties of the cyclic, tertiary 2,2,6,6 tetramethylpiperidine groups that are disclosed as nitrogen containing modifiers.
U.S. Pat. No. 3,867,478 discloses that the use of polyamides containing tertiary amino groups in polyesters results in brown, discolored fibers after melt-blending and melt-spinning. The brightness of the dyed fibers is also reported as reduced. U.S. Pat. No. 3,867,478 discloses the use of phosphorus compounds to improve the dyeability of polyesters containing tertiary amino groups.
Japanese Kokai No. 47-32184 discloses that nitrogen containing polyesters are difficult to acid-dye because the addition of sufficient nitrogen dye sites into the polymer causes coloring in the polymer and decreases physical properties. Lower amounts of basic nitrogen in polyesters are said to be insufficient to develop adsorption toward the acidic dye. The addition of benzene derivatives to the dye bath is proposed to improve the dyeability of the fibers.
Although, as described above, substantial work has been done with respect to the use of tertiary amine compounds to enhance the dyeability of polyesters, secondary aliphatic amines have generally been used in polymeric compositions as chain branching agents or crosslinkers because of their functionality. U.S. Pat. No. 4,145,473 to Samuelson, et al. discloses the use of bis-(hexamethylene)triamine as a branching agent to increase the viscosity of polymer compositions used in melt spinning fibers.
U.S. Pat. No. 5,068,283 discloses a method for producing a thermoplastic resin wherein a saturated polyester resin and an epoxy group-containing ethylene copolymer are melt-kneaded into a composition and then further melt kneaded with a polyfunctional compound which carries out a partial cross-linking reaction. The polyfunctional compounds may be an amine. However, as disclosed in U.S. Pat. No. 5,322,923, the presence of structural derivatives of bis-(hexamethylene)triamine in amounts greater than 0.5 weight % has been shown to cause an undesirable increase in the viscosity characteristics of copolyamides used as molding compositions.
Methods that relate to treating a polyester with a dye composition containing nitrogen compounds, as opposed to including a nitrogen containing additive in the polyester, have also been proposed. U.S. Pat. No. 3,932,126 discloses a process for acid dyeing shaped or preformed polyester materials by applying an aqueous solution or printing paste of one or more acid dyes, various organic nitrogen compounds and organic carboxylic acids. The impregnated polyester material is dried and then heated. The preferred organic nitrogen compounds include alkyleneamines, alkanolamines and alkylamines.
All of the aforementioned documents are incorporated herein by reference.
It is desirable to have acid-dyeable nitrogen-containing polyester compositions which may be easily processed into fibers, films or other shaped articles and acid-dyed without expensive additives, special solutions, and/or complicated application procedures.